Damping system for mechanical shutter

ABSTRACT

A damping system for an electromagnetically operable rotary shutter includes a damper for arresting the motion of a pivotally supported shutter actuating drive arm. The damper has a first portion composed of an ultrahigh density polyethylene and a second portion composed of a damped polyurethane that are arranged to strike one against the other during operation of the shutter. Moreover the first portion of the damper has a straight edge and the second portion has a surface that is curved so as to maintain substantially a point contact between the two portions throughout the duration of the impact between the two. The combination of materials and configuration of the surfaces of the two portions provides energy absorption while avoiding the adherence of the two portions upon impact.

TECHNICAL FIELD

The present invention relates generally to dampers for lightweightmechanical assemblies and more particularly to a damper for a mechanicalshutter such as a photographic shutter.

BACKGROUND ART

Mechanical assemblies having moving parts frequently require damping toprotect the parts from damaging impacts and to increase the life andreliability of the assemblies. This is particularly true where themechanical assembly is lightweight and the impact is repetitive and at ahigh rate of speed. Electrically operated lens shutters used in varioustypes of photographic and laboratory equipment meet these criteria. Forexample, a shutter can open and close in a fraction of a second.Electronically operated shutters can operate at frequencies of 2 to 400cycles per second and higher.

Lens shutters generally are of two types. In one type, a so called“guillotine” shutter has one or two thin, metal blades or leavesarranged to cover a lens opening. Pivot connections allow each blade toswing between a closed position where the blades cover the lens openingand an open position where the blades are drawn aside from the lensopening.

In a second type, a plurality of pivotally mounted blades, usually five,are arranged around the lens. Each blade is connected to a rotatablering. In the operation of these rotary shutters, the rotation of thering in one direction causes the blades to swing in unison to an openposition. Counter rotation of the ring swings the blades to a closedposition over the lens opening after exposure.

It is common in the first type of shutter to provide a shock absorber ordamper that absorbs the impact as the blades are pivoted between theopen and closed positions. In this respect, reference is made to U.S.Pat. No. 3,595,553 and No. 3,664,251, the disclosures of which areincorporated herein by reference. As disclosed in these references, theshock absorber operates to stop the shutter blade very rapidly, yetsoftly without damage and with little or no bounce. To Applicant'sknowledge, a comparable shock absorbing system has not been used inconnection with the rotating ring type of shutters.

One material known to have damping characteristics suitable for use inthe damping system of photographic shutters is an ISOLOSS® high densitymolded product made by Aearo Company. The ISOLOSS® products are highdensity damped polyurethane thermoset polymers. Sheets and molded partsof this material have been used in a variety of applications relating tonoise, shock and vibration reduction. The material has favorablehysteretic damping properties, good compliance and is able to absorb andstore mechanical energy while effectively dissipating it in the form ofheat.

Dampers made from this polyurethane molded material have been used forsome time in combination with other materials such as metals and Tefloncoated metal and have provided good results in some applications.However, one disadvantage of the polyurethane molded shock absorbingformulations is that they have a rubbery characteristic and tend tostick to the surfaces that they impact while performing the dampingfunction. In an attempt to remedy this, the impact surface often iscoated with Teflon. A Teflon coated surface can reduce or eliminate thesticking when contacting the polyurethane molded damper, however, theTeflon coated surface introduces other problems. Teflon tends to scaleand form a powdery residue somewhat like talcum powder in itsconsistency. In many applications the residue is not harmful but, insome applications, such as optical shutters, the residue may find itsway to the surfaces of optical components such as lenses. This powder onthe surface of the lens is detrimental to the operation of the lens.

Accordingly, it is an object of the present invention to provide animproved damping system for photographic shutters and in particular,high speed rotary shutters.

Another object of the present invention is to provide a damping systememploying a polyurethane molded damper that eliminates sticking of thedamper to the impact surface.

A further object is to provide a damping system having an increasedoperational life.

DISCLOSURE OF INVENTION

In the present invention a rotary shutter is provided with a dampingsystem wherein the swinging motion of the shutter drive arm through anarcuate path of travel is arrested by a detent positioned to engage amember carried by the drive arm. The member is a beam that is generallytriangular in cross section. Fixed to each side of the beam is a damperformed of a highly damped polyurethane thermoset material. Impact of thedampers against the detent arrests the movement of the drive arm.

The impact surface of the detents comprises a bumper composed of anultra high molecular weight polyethylene. This material, together withthe shape and disposition of the bumper and damper provide a limitedcontact area. Having a limited contact area concentrates the impactenergy and improves the efficiency of the damping system. When thedamper is struck, the material at the point of impact undergoes atransformation from a glass phase to a rubber phase and it is the rubberphase that tends to stick to the impact surface. By limiting the area ofcontact to a line or more preferably a point contact, the potential“sticky” area is reduced to a minimum.

Accordingly, by careful selection of the shape, materials andarrangement of the damper and bumper, sticking is virtually eliminated.Life testing demonstrates that the components have a much greater lifethan heretofore achieved with other components. Damping characteristicsof the combination are close to ideal for electromechanical shutters andlikely for other applications in that the design essentially eliminatesbounce or rebound after impact.

Accordingly, the present invention may be characterized in one aspectthereof by a damping system for arresting motion of a small mass such asa photographic shutter or the like driven by a drive arm mounted forswinging motion through an arcuate path of travel. The damping systemincludes a detent having opposite ends arranged to arrest motion of thearm at each end of the path of travel. In this respect the opposite endsof the detent carry bumpers formed of a high molecular weightpolyethylene that are disposed to impact a damper on the drive arm, thedamper being composed of a high density polyurethane thermoset material.Both the bumper and damper are shaped to provide substantially pointcontact during the duration of the engagement between the damper and thebumper.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front elevation view of a shutter incorporating the dampingsystem of the present invention;

FIG. 2 is a perspective view on an enlarged scale of a portion of FIG.1;

FIG. 3 is a plan view of the structure shown in FIG. 2 with portionsremoved for clarity;

FIG. 4 is a view taken generally along lines 4-4 of FIG. 3;

FIG. 5 is a view on an enlarged scale of a portion of FIG. 4 showing thedisposition of components with the shutter in a closed position; and

FIG. 6 is a view on an enlarged scale of a portion of FIG. 3.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Referring to the drawings, FIG. 1 shows a rotary shutter generallyindicated at 10 incorporating the damping system of the presentinvention. It should be appreciated that various components, bracketsand wiring harnesses of the shutter assemble have been omitted forclarity. For purposes of orientation, the shutter includes a base plate12 having a central aperture 14. Supported at the underside (not shown)of the base plate are a plurality of shutter blades 16, portions ofwhich are seen through the aperture. The rotary shutter is conventional.It is sufficient for purposes of the present invention to say that theshutter blades are operatively attached to a driver plate (not shown)that rotates with respect of the base plate. Rotation of the driverplate in one direction moves the shutter blades aside and opens theaperture. Reciprocal rotation of the driver plate moves the shutterblades back to the position shown in FIG. 1 wherein the aperture isclosed.

The means for operating the driver plate includes an electromagneticactuator 18 mounted to the base plate. The actuator includes an armature20 that engages a laterally extending rocker arm 22. The rocker armengages a drive arm 24. The drive arm is flat and formed of very thinsheet metal to minimize mass and is pivotally supported so its end 26moves in an arcuate path of travel. At its end 26, the drive arm isconnected to a link 28. The link has a connector 30 that extends throughan elongated opening 32 in the base plate for connection to the driverplate.

The swinging movement of the drive arm 24 is damped by the dampingsystem of the present invention generally indicated at 34. As best seenin FIGS. 2 and 3 the damping system includes a pair of bumpers 36attached to a shaped spring wire 38. One of the bumpers is an innerbumper 36A and the outer is an outer bumper 36B.

The spring wire that supports the bumpers preferably is formed of pianowire about 0.020 inches in diameter and is shaped to form a torsionspring. In this respect the spring wire is formed with a central spine40 that is bifurcated (FIG. 3). The two portions 42, 44 of thebifurcated spine 40 are joined at one end 46 and are spaced apart andunjoined at an opposite end 48. Each of the two portions 42, 44 in turnis bent to form opposed, generally U-shaped arms 50 extending outwardfrom the central spine 40. As best seen in FIGS. 4 and 5, the oppositeends 52 of the U-shaped arms are each bent downward from the plane ofthe central spine 40 and support the bumpers below the plane of thecentral spine 40.

As formed, the arms 50 of the spring wire are bent downwardly from theplane of the central spine 40. However, as shown in FIGS. 1 and 2, thespring wire 38 is carried by a stop plate 54 that is disposed beneaththe arms and engages the arms to force them to assume an orientationthat is closer to the plane of the spine. This pre-loads the arms 50 toprovide a bias urging the arms to pivot downwardly from the plane of thecentral spine 40.

The stop plate in turn is rigidly fixed to a relatively heavy and rigidsupport wire 56. The support wire 56, with a diameter of 0.050 inches,is over twice the diameter of the spring wire 38. The ends 58, 60 of thesupport wire are fixed as rigidly as possible to the base plate 12(FIG. 1) so as to minimize as much as possible the flexure of thesupport wire.

As best seen in FIGS. 2, 3 and 6, each bumper 36 is generally oval inshape. The ends of the oval shape are each provided with a groove 62.These grooves receive the end 52 of the U-shaped arms for attaching thebumpers to the spring wire 38.

The damping system 34 is further shown in FIGS. 3, 4 and 5 to includecomponents carried by the drive arm 24, which interact with the bumpers36 and the spring wire 38. These components include a beam 64 that isfixed to a surface of the flat drive arm adjacent its end 26. The beamis generally triangular in cross section and the two upstanding sides orlegs of the triangular beam extend upwardly from the drive arm and intothe space between the downwardly bent ends 52 of the spring wire. Fixedto and extending outward from each of the upstanding legs is a damper68. One of the dampers is an inner damper 68A and the other is an outerdamper 68B. Each damper is generally triangular in cross section and isfixed to the beam such that a longitudinally extending corner 70 of eachdamper is disposed to contact one of the bumpers 36 (FIGS. 5 and 6).

In a start position with the shutter closed, the corner 70 of the innerdamper 68A is in contact with the inner bumper 36A (FIGS. 4 and 6). Tooperate the shutter, the electromagnet 18 is energized and the armature20, operating through the rocker arm 22, pivots the drive arm 24 so itsend 26 is swung upwardly as viewed in FIG. 1. This pulls the connectinglink 28 and rotates a driver plate (not shown) to open the shutter.Pivoting the drive arm carries the outer damper 68B forward and intocontact with the outer bumper 36B wherein the engagement of one againstthe other arrests the motion of the drive arm. When the electromagnet isde-energized, a spring 72 returns the drive arm back to the startposition to close the shutter. The return motion of the drive arm thenis arrested by the engagement of the inner damper 68A against the innerbumper 36A.

In a shutter having an aperture of 45 mm the operating speed of theshutter can be up to 5 Hertz and the speed increases as the aperturesize decreases. Operating speeds of up to 400 hertz or more are possiblein shutters having an aperture of 2 mm. Accordingly, it is important toarrest the forward and reverse motion of the drive arm quickly, smoothlyand with little or no bounce. Several aspects contribute to thesuccessful operation of the damping system of the present invention. Forexample, one of the damper and bumper is formed of a highly dampedpolyurethane thermosetting resin that provides high performance damping,isolation, and shock and motion control with a loss factor in excess of1.0. A preferred material is a urethane solid having the followingproperties:

Normal Hardness (ASTM D2240) Shore A Durometer Impact at 73° F. (23° C.)of about 58,

Glass transition temperature (ASTM D575) of about 18° F. (−8° C.),

Maximum loss factor at 10 Hz and 54° F. (12° C.) of about 0.94,

Rebound (ASTM D2632) Bashore Resilience

-   -   Rebound, 1st impact @ 20° C. of about 4.5%    -   Rebound, 2^(nd) impact @ 20° C. of about 0.0%,

Compression Load Deflection (ASTM D575)

10% Deflection about 82 psi (565 kPa)

20% Deflection about 180 psi (1241 kPa)

30% Deflection about 305 psi (2103 kPa)

Compression Modulus about 845 psi (5826 kPa).

A suitable material is ISOLOSS® HD made by Aearo Company.

The other of the damper and bumper is formed of an ultra high molecularweight polyethylene (UHMWPE) having a molecular weight in the range of 3to 6 million. Such a material typically has a density of at least 0.930g/cm³ and up to 0.965 g/cm³. Surprisingly, such a high molecular weightpolyethylene provides effective damping when used together with thepolyurethane despite the hardness of the polyethylene, which isconsidered a detriment to effective damping.

In a preferred arrangement the bumper is made of the UHMWPE whereas thedamper is formed of the polyurethane. The polyethylene is extrudable toa desired shape of the bumper, as described hereinbelow, whereas theurethane material is not extrudable and must be molded to shape. Also,the urethane is readily attachable to the beam with an adhesive whereasan adhesive attachment of the polyethylene to the beam does not hold upover time and under the stress of repeated impacts.

The present invention also has the components of the damping systemarranged to provide substantially point contact between bumper 36 andthe damper 70 during the entire time interval of contact between thetwo. This is accomplished by providing the bumper with an oval shape asshown and the damper with a longitudinally extending corner 70. Thearrangement of the straight corner 70 of the damper striking against thecurved surface of the oval bumper (FIG. 6) maintains substantially pointcontact for the duration of the contact time. Limiting the engagement tosubstantially point contact improves the efficiency of the dampingsystem.

A further contribution to the impact absorbing characteristics of thedamping system results from the loading of the arms 50. As describedabove, the arms are loaded so they are biased in a downward direction.Accordingly an impact of a damper 68 against a bumper 36 that tends torotate the arm 50 upwardly about the central spine is resisted by thedownward bias of the arm. Furthermore, as shown in FIG. 5, each end 52of the U-shaped arm 50 is bent downward at an angle of about 77° orwithin about 13° of a line perpendicular to the plane of the arm 50.This allows the impact of the damper to be partly absorbed by both anupward flexing in unison of the arm 50 and of the bifurcate centralspine 40 of the spring wire. The angle is maintained to insure that thecorner 70 of the damper strikes the approximate center of the bumper 36Aso the two do not disengage as the bumper deflects upwardly against theresistance offered by the urging of the downward bias of the arm. Theangle also prevents the adhesion of the two materials during the contactcompression phase when the beam is moved causing the damper corner toimpact the bumper.

While all the components as described cooperate to provide an effectivedamping system, it was found that forming the damper and bumper ofpolyurethane and high molecular weight polyethylene respectivelycontributed significantly to the effectiveness of the damper. Inparticular, these materials served to increase the operational life ofthe shutter by six times from one to six million operations whilevirtually eliminating the adhesion of the damper and bumper materialswithout the use of either anti-stick materials such as Teflon orlubricants.

1. A rotary photographic shutter or the like comprising a plurality ofshutter blades movable between an open and a closed position, anactuator, a linkage coupled between the actuator and the shutter bladesfor moving the shutter blades between the open and closed positions, anda damper engaging the linkage and isolated from contact with the shutterblades, the damper being operable to damp motion of the shutter bladeswithout contacting them.
 2. The rotary photographic shutter of claim 1,further comprising a bumper, the bumper and the damper being shaped toprovide substantially point contact therebetween at the one of the openand closed positions.
 3. The rotary photographic shutter of claim 1,wherein the linkage comprises a drive arm, and the damper is disposed onthe drive arm and configured to engage a bumper supported by the baseplate.
 4. The rotary photographic shutter of claim 1, further comprisingan inner bumper joined to an outer bumper by a biased connector.
 5. Therotary photographic shutter of claim 4 wherein the biased connectorcomprises a spring wire, the spring wire being connected to a stopplate.
 6. The rotary photographic shutter of claim 4, wherein the drivearm is configured to travel in an arcuate path between the inner bumperand the outer bumper.
 7. The rotary photographic shutter of claim 4further comprising an additional damper, the damper and the additionaldamper configured to travel in an arcuate path between the inner bumperand the outer bumper.
 8. The rotary photographic shutter of claim 1wherein the linkage configured to oscillate between an outer bumper andan inner bumper.
 9. The rotary photographic shutter of claim 1 whereinthe linkage is configured to pivot about an axis offset from a centralaxis of the rotary photographic shutter.
 10. The rotary photographicshutter of claim 1 further including an outer bumper and an innerbumper, the outer and inner bumpers being substantially entirelydisposed on one side of a shutter opening defined by the shutter blades.11. A rotary photographic shutter comprising: a) a base plate having acentral aperture; b) a rotating ring: c) a plurality of shutter bladessupported by the base plate and coupled to the rotating ring for openingand closing the aperture; d) an actuator coupled to the rotating ring;e) a linkage coupled between the actuator and the rotating ring; and f)a damping system on the base plate engaging the linkage, isolated fromcontact with the shutter blades, and operable to dampen the opening andclosing of the shutter blades.
 12. The rotary photographic shutter ofclaim 11, wherein the linkage comprises: a) a drive arm pivotallysupported on the base plate to swing back and forth through a definedarc, the swing of the drive arm in one direction acting to move theshutter blades to an open position and the swing in a return directionacting to move the shutter blades to a closed position; and b) whereinthe damping system engages the drive arm for arresting the swing of thedrive arm at each end of the arc.
 13. A The rotary photographic shutterof claim 12 wherein the damping system comprises: a) a detent havingopposite ends disposed to arrest the swinging movement of the drive armat each end of the swing; c) bumpers on each of the opposite ends of thedetent; and d) at least one damper on the drive arm positioned to strikeand engage against each of the shaped bumpers at the limits of the swingof the drive arm.
 14. The rotary photographic shutter of claim 13wherein the bumpers and the damper are shaped to provide substantiallypoint contact therebetween during the duration of the engagement.
 15. AThe rotary photographic shutter of claim 13 wherein the damping systemcomprises: a) bumpers carried by one of the drive arm and the base platecomposed of a polyethylene having a molecular weight of 3 to 6 million;and b) a damper on the other of the drive arm and base plate composed ofa polyurethane material that under goes a transformation from a glassphase to a rubber phase when it strikes the bumpers.
 16. The rotaryphotographic shutter of claim 11 wherein the damping system comprises abumper and a damper, the bumper and the damper being shaped to providesubstantially point contact therebetween at one of an open position ofthe shutter blades and a closed position of the shutter blades.
 17. Therotary photographic shutter of claim 16, wherein the linkage comprises adrive arm configured to assist in opening and closing the shutterblades, wherein the damper is disposed on the drive arm.
 18. The rotaryphotographic shutter of claim 16 wherein the damping system comprises afirst bumper and a second bumper, the damper being configured to travelbetween the first bumper and the second bumper.
 19. A rotaryphotographic shutter, comprising: a) a plurality of shutter bladesmoveable between an open and closed position; b) a drive arm configuredto move the shutter blades between an open position and a closedposition; and c) a damping system comprising a bumper and a damper, oneof the bumper and the damper being mounted on the drive arm, and thebumper and the damper being shaped to provide substantially pointcontact therebetween at the one of the open and closed positions whereinthe bumper comprises an inner bumper and an outer bumper, the damperbeing configured to travel along a path between the inner bumper and theouter bumper.
 20. The rotary photographic shutter of claim 19 whereinthe path is an arcuate path.
 21. A rotary photographic shutter,comprising: a) a plurality of shutter blades moveable between an openand closed position; b) a drive arm configured to move the shutterblades between an open position and a closed position; and c) a dampingsystem comprising a bumper and a damper, one of the bumper and thedamper being mounted on the drive arm, and the bumper and the damperbeing shaped to provide substantially point contact therebetween at theone of the open and closed positions wherein the damper comprises aninner damper connected to an outer damper.
 22. A rotary photographicshutter, comprising: a) a plurality of shutter blades moveable betweenan open and closed position; b) a drive arm configured to move theshutter blades between an open position and a closed position; and c) adamping system comprising a bumper and a damper, one of the bumper andthe damper being mounted on the drive arm, and the bumper and the damperbeing shaped to provide substantially point contact therebetween at theone of the open and closed positions wherein the damper is isolated fromcontact with the shutter blades.